This invention relates to a circuit arrangement for the operation of at least one high-pressure gas discharge lamp by means of a pulsatory supply current having a pulse recurrence frequency between 50 and 2000 Hz and a duty cycle between 0.2 and 0.8.
Such a circuit arrangement for the operation of high-pressure sodium vapour discharge lamps is known, for example, from U.S. Pat. No. 4,128,789. A pulse operation can also be used, however, in high-pressure mercury vapour discharge lamps and in high-pressure metal halide vapour discharge lamps. For the pulse operation, both unipolar and bipolar pulses are suitable (DE-PS 26 57 824). An advantage of the pulse operation of high-pressure gas discharge lamps in the aforementioned frequency range consists in that the lamps do not exhibit any acoustic resonance, at least in part of the frequency range. Any acoustic resonance would become manifest in flickering of the luminous arc (DE-PS that 31 11 561). It is further known from this DE-PS to avoid acoustic resonance in high-pressure gas discharge )amps operated at a high-frequency voltage, the high-frequency sinusoidal fundamental wave of 15 to 50 kHz has superimposed on it its third harmonic. The light output and the coulour temperature of lamps operated in this manner are not so favourable, however, as compared with pulse operation.
In the case of pulse operation of high-pressure gas discharge lamps, the stabilization of the lamp current solely by passive elements, such as, for example, a choke coil, is very impractical. Instead, the current stabilization must rather be obtained by electronic means.
With pulse operation of high-pressure gas discharge lamps having electronic ballast units, however, a so-called flickering of the lamps often occurs. This flickering comes about because the luminous flux of the lamps is varied periodically or abruptly. Although the luminous arc itself then remains stable, the luminance of the lamp fluctuates to such an extent that the human eye can observe these variations.